IN-VITRO STIMULATION OF RENAL TUBULAR P-AMINOHIPPURATE TRANSPORT BY DEXAMETHASONE IN KIDNEY TISSUE OF IMMATURE AND ADULT RATS

The in vitro stimulation of the accumulation of p-aminohippurate (PAH) was investigated in renal cortical slices of 10- and 55-day-old rats. For this goal tissue slices were incubated for 24 hours in Williams m edium E containing different concentrations of dexamethasone (0.01-5 m u mol). After this incubation period slices were placed in PAH contain ing Cross-Taggart medium and PAH uptake into the kidney tissue was mea sured for two hours. In both immature and adult rat's tissue slices an active PAH accumulation can be proven after 24 hours incubation witho ut hormone substitution. In both age groups the accumulation capacity after 24 hours incubation reaches about 40-60 % of that of acute two h ours incubation experiments (slice to medium ratios after two hours of incubation: immature rats: 9.5 +/- 0.4; adults: 11.4 +/- 0.3). In the acute incubation experiments there was no influence of dexamethasone on PAH accumulation whereas after 24 hours incubation dexamethasone si gnificantly increases the PAH uptake capacity in a concentration depen dent manner: 10- and 55-day-old rats: 26 and 36 (65) % increase, respe ctively. It can be concluded that 1.) a stimulation of tubular transpo rt capacity can be performed in vitro, and 2.) discrepancies between i n vitro and in vivo stimulation exist concerning PAH accumulation in r enal cortical slices.